Factors relevant to control of fueling of a compression ignition (diesel) engine include the timing of an injection of fuel into a combustion chamber, the duration of the fuel injection, and the pressure at which the fuel is injected. The physical construction of various devices in the fueling system, such as the fuel injectors, and combustion chamber geometry are also relevant factors.
A known electronic engine control system comprises a processor-based engine controller that processes data from various sources to develop control data for controlling certain functions of the engine, including fueling of the engine by injection of fuel into engine combustion chambers. A known diesel engine that powers a motor vehicle has an oil pump that delivers oil under pressure to an oil rail serving electric-actuated fuel injection devices, or simply fuel injectors, that use oil from the oil rail to force injections of fuel. The pressure at the oil rail is sometimes referred to as injection control pressure, or ICP, and that pressure is under the control of an appropriate ICP control strategy that is an element of the overall engine control strategy implemented in the engine control system.
Certain known fuel injectors contain electric-actuated valves that control the delivery of oil that has been pumped to an oil rail at ICP to pistons that force fuel into the engine combustion chambers via plungers. Certain fuel injectors are capable of pressure amplification that can develop very high injection pressures. Moreover, certain fuel injectors have the capability to digitally modulate pressure during an injection (sometimes referred to as rate-of-injection, or ROI, shaping).
The on-going development of engine combustion technology is striving to improve the quality of combustion processes so that lesser amounts of undesired constituents are present in engine exhaust. In order to attain compliance with standards that may be applicable to tailpipe emissions, even improved in-cylinder combustion processes may still require that exhaust systems include one or more types of exhaust after-treatment devices.
One such after-treatment device is a diesel particulate filter (DPF). A DPF is capable of physically trapping diesel particulate matter (DPM) in exhaust gas passing through the exhaust system from the engine to prevent significant amounts of DPM from entering the atmosphere.
Another after-treatment device is a NOx adsorber catalyst, sometimes called a lean NOx trap, or LNT. It removes significant NOx from exhaust gas.
Such after-treatment devices add cost to an engine and hence to any new automotive vehicle propelled by such an engine. From time to time the after-treatment devices also require regeneration. While some regeneration occurs naturally, the level of trapped products of combustion eventually reaches a point where the after-treatment device requires forced regeneration. Forced regeneration typically involves operating the engine in a way that creates elevated exhaust temperatures. The creation of such temperatures of course requires the combustion of additional fuel which penalizes fuel economy.
Proposed solutions for compliance with tailpipe emission levels defined by current EPA regulations for MY 2010 include the use of wall flow particulate traps and NOx after-treatment devices, such as SCR, LNT, or LNC, and combinations thereof. Other proposed solutions involve the use of homogeneous charge compression ignition (HCCI) with limited Brake Mean Effective Pressure (BMEP) capability, or very high diluent concentrations (O2 concentration<about 14%). Reducing oxygen concentration of an air/fuel mixture, typically by control of recirculated exhaust (EGR), slows kinetics of the combustion process, allowing more time for fuel and charge air to mix before combusting. But implementation of that type of strategy is made at the cost of increasing the complexity of the charge management system and increasing total system heat rejection. BMEP refers to the average pressure that would need to be present in a cylinder to realize the observed brake torque produced by the engine.